fix(schema): add missing FK indexes and constraints

[adityathebe]

Add 74 missing indexes on foreign key columns across all schema files.
PostgreSQL does not auto-create indexes for FK columns, causing full
sequential scans on joins, cascade deletes, and filtered queries.

Also add two missing FK constraints:

• logging_backends.agent_id -> agents.id
• external_roles.scraper_id -> config_scrapers.id

Agent Conversation: https://pi.dev/session/#23fc14d97915172bb47a9799228d080b

[github-actions]

Benchstat

Base: 92eb3b0c7ecea2104315c1078bec3d8dfbf32074
Head: 3988d940c7ada1a296eb30a2b45a115be253dd16

goos: linux
goarch: amd64
pkg: github.com/flanksource/duty/bench
cpu: AMD EPYC 7763 64-Core Processor                
                                                │ bench-base.txt │          bench-head.txt           │
                                                │     sec/op     │   sec/op     vs base              │
Main/Sample-15000/catalog_changes/Without_RLS-4      5.453m ± 4%   5.613m ± 8%  +2.93% (p=0.002 n=6)
Main/Sample-15000/catalog_changes/With_RLS-4         130.4m ± 0%   128.6m ± 1%  -1.39% (p=0.009 n=6)
Main/Sample-15000/config_changes/Without_RLS-4       5.471m ± 1%   5.538m ± 6%  +1.23% (p=0.041 n=6)
Main/Sample-15000/config_changes/With_RLS-4          128.2m ± 0%   128.8m ± 0%  +0.49% (p=0.015 n=6)
Main/Sample-15000/config_detail/Without_RLS-4        3.947m ± 1%   3.929m ± 2%       ~ (p=0.485 n=6)
Main/Sample-15000/config_detail/With_RLS-4           125.4m ± 0%   125.4m ± 1%       ~ (p=0.699 n=6)
Main/Sample-15000/config_names/Without_RLS-4         12.92m ± 2%   13.08m ± 1%       ~ (p=0.093 n=6)
Main/Sample-15000/config_names/With_RLS-4            125.8m ± 0%   126.6m ± 1%  +0.61% (p=0.002 n=6)
Main/Sample-15000/config_summary/Without_RLS-4       63.43m ± 1%   62.95m ± 1%       ~ (p=0.065 n=6)
Main/Sample-15000/config_summary/With_RLS-4          741.0m ± 0%   735.9m ± 1%  -0.68% (p=0.002 n=6)
Main/Sample-15000/configs/Without_RLS-4              7.387m ± 1%   7.255m ± 4%       ~ (p=0.065 n=6)
Main/Sample-15000/configs/With_RLS-4                 124.6m ± 2%   125.2m ± 1%       ~ (p=0.093 n=6)
Main/Sample-15000/analysis_types/Without_RLS-4       3.921m ± 3%   3.921m ± 2%       ~ (p=0.818 n=6)
Main/Sample-15000/analysis_types/With_RLS-4          3.977m ± 3%   3.923m ± 1%  -1.36% (p=0.002 n=6)
Main/Sample-15000/analyzer_types/Without_RLS-4       3.758m ± 2%   3.745m ± 1%       ~ (p=0.180 n=6)
Main/Sample-15000/analyzer_types/With_RLS-4          3.786m ± 4%   3.768m ± 4%       ~ (p=0.132 n=6)
Main/Sample-15000/change_types/Without_RLS-4         5.553m ± 4%   5.359m ± 3%  -3.50% (p=0.009 n=6)
Main/Sample-15000/change_types/With_RLS-4            5.475m ± 3%   5.416m ± 3%       ~ (p=0.589 n=6)
Main/Sample-15000/config_classes/Without_RLS-4       3.323m ± 1%   3.291m ± 4%       ~ (p=0.180 n=6)
Main/Sample-15000/config_classes/With_RLS-4          123.9m ± 0%   125.5m ± 0%  +1.29% (p=0.002 n=6)
Main/Sample-15000/config_types/Without_RLS-4         4.018m ± 2%   3.992m ± 6%       ~ (p=0.699 n=6)
Main/Sample-15000/config_types/With_RLS-4            125.5m ± 0%   124.5m ± 2%       ~ (p=0.394 n=6)
geomean                                              19.51m        19.46m       -0.28%

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch fix/schema-missing-indexes-and-fk-constraints

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